Field of the Invention
The present invention relates to a development device that is adaptable to an image forming apparatus using an electrophotographic image forming process, such as a laser beam printer, a copying machine, or a facsimile device, and an image forming apparatus.
Description of the Related Art
A two-component development system using a mixture of non-magnetic toner and magnetic carriers as developer has widely been used in a development device mounted to an image forming apparatus using toner as developer.
With the two-component development system described above, a developer is carried on the surface of a development sleeve due to magnetic force of a magnet roller stored in the development sleeve (developer bearing member), and the amount of the carried developer is regulated by a development blade to form a thin developer layer on the development sleeve. Then, the developer layer is conveyed to a development region facing a photosensitive drum due to the rotation of the development sleeve, and electrostatically adsorbed on the photosensitive drum with the developer being napped in a brush chain due to the magnetic force of the magnet roller. Thus, an electrostatic latent image is developed.
In the development device described above, a configuration for stabilizing an amount of developer carried on a development sleeve has conventionally been proposed. For example, Japanese Patent Laid-Open No. 2015-169696 discloses a configuration in which magnetic force in a tangential direction relative to the surface of a development sleeve is oriented in the direction same as the rotation direction of the development sleeve within a region from a scooping pole which scoops developer up to the development sleeve to a regulation pole which is a magnetic pole near the development blade. With this configuration, the developer is effectively conveyed by the development sleeve, whereby the amount (coating amount) of developer carried on the development sleeve is stabilized.
In general, a magnet roller has, for a peak position of a magnetic flux density in the normal direction relative to the surface of a development sleeve, an error of ±3° in the rotation direction of the development sleeve from a set peak position and a fluctuation of ±2° for a half width, as a component tolerance. Therefore, the magnetic flux density in the normal direction has a maximum fluctuation of ±5° on a region facing the development blade.
Herein, a napping angle of developer regulated by the development blade is defined by arctan (Br/Bθ) that is an arctangent function of a magnetic flux density Br which is a component in the normal direction and a magnetic flux density Bθ which is a component in the tangential direction, in the magnetic flux density exerted from the magnet roller. Therefore, when the magnetic flux density Br of a magnetic pole in the normal direction or the magnetic flux density Bθ in the tangential direction varies due to the component tolerance, the napping angle varies, so that the amount of developer regulated by the development sleeve varies.
Therefore, even when an effort is made to obtain a desired magnetic force distribution as in the configuration disclosed in Japanese Patent Laid-Open No. 2015-169696, the distribution of the magnetic flux density Br or the distribution of the magnetic force varies due to the component tolerance to cause a machine difference in an amount of developer regulated by the development blade and an amount of developer conveyed to a development region. This might adversely affect image property.
Specifically, if a regulation amount of developer is less than a desired amount, a coating amount of developer on the development sleeve increases, by which a fog on a photosensitive drum, overflow of developer, or a lock due to an increase in torque is likely to be caused. On the other hand, if a regulation amount of developer exceeds a desired value, a coating amount of developer on the development sleeve is decreased, by which it is likely that a required image density is not output.